Winches can be used for mooring a vessel. Such a vessel may be a ship, a boat or generally a craft designed for water transportation in a sea, an ocean, a lake, a river, a channel, a canal, or any parts thereof, for example.
Such a winch used for the mooring may comprise a winch drum which is rotatable about an axis of rotation thereof and may be used for spooling a spoolable medium, which is to be connected to a point of mooring. The spoolable medium may comprise a cable, a rope, a wire or a chain, for example. The point of mooring may be any point where the vessel can be moored, such as a mooring-post of a vessel landing place, e.g. a port or a pier, or an anchor or a buoy, for example. The winch used for the mooring may further comprise an electric motor drive comprising an electric motor, which is configured to rotate the winch drum about the axis of rotation thereof during spooling in or spooling out of the spoolable medium. The electric motor drive can be an AC drive or a DC drive and the electric motor can be an AC motor, such as an asynchronous motor (induction motor) or a synchronous motor, or a DC motor, respectively, for example.
In a vessel, the mooring functionality of the winch used for mooring can control the spoolable medium that holds the vessel in place at the point of mooring by means of the electric motor drive. When the vessel is being moored, the tension of the spoolable medium between the vessel and the point of mooring can be automatically adjusted by suitably controlling the electric motor drive that controls the winch used for mooring. The tension of the spoolable medium between the vessel and a point of mooring should be kept at an appropriate level. If the spoolable medium between the vessel and the point of mooring is too loose, the vessel will not stay in place, and if the spoolable medium is too tight, the spoolable medium might break or the operation might become unstable.
The electric drive can be controlled such that when the tension of the spoolable medium between the vessel and a point of mooring is outside a predetermined hysteresis zone, the spoolable medium is either tightened (spooled in) or loosened (spooled out) at a predetermined constant driving speed of the winch drum towards a predetermined tension set point. And when the tension of the spoolable medium between the vessel and the point of mooring has been inside a predetermined dead band zone, located within the hysteresis zone, for a certain predetermined period of time, the tightening or loosening is stopped.
Controlling the adjustment of the spoolable medium smoothly close to the predetermined tension set point is desirable. However, in the above solution, oscillations around the predetermined tension set point can easily occur and resulting sudden stops can be harmful to the mechanics of the winch and the spoolable medium, for example.